Shower base



FIG. 1 is a perspective view taken from the front and left side of a shower base showing my new design;

FIG. 2 is a top plan view;

FIG. 3 is a bottom plan view;

FIG. 4 is a right side elevation;

FIG. 5 is a left side elevation;

FIG. 6 is a front elevation; and,

FIG. 7 is a rear elevation. 

The ornamental design for a shower base, as shown. 